video: fbdev: sh_mobile_lcdcfb: add COMPILE_TEST support

Add COMPILE_TEST support to sh_mobile_lcdcfb driver for better compile
testing coverage.

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patchwork.freedesktop.org/patch/msgid/d98fea18-b72e-6d0f-33ac-1421738bd12b@samsung.com